Heating ventilation and air conditioning (HVAC) systems require both a supply duct system for output to the occupied space of a building structure and a return air duct system to re-circulate conditioned back to the HVAC system. Supply ducts have grilles that serve to diffuse the air going into the room and return air ducts have grilles that hide the view of the ducts or filters, as the case may be. To clean the circulated air, an HVAC system has filters in one of two locations in the return air portion accessible for periodic cleaning and replacement. The accessible locations are either immediately behind the return air grille or at the HVAC unit, which is typically in an attic or basement. When the filter is located just behind the grille, the grille assembly needs to provide easy access for filter removal and replacement. When the filter is located at the HVAC unit, the grille assembly needs to provide easy access for duct cleaning since dirty air is being returned through those ducts to the HVAC system.
Since return air grilles are most often prominently located and visible in the building, they do not commonly have visible screws or latches to hold them in place, unless they are “fixed” grilles which use visible screws to hold them in place. Even then, hiding the screw heads is preferable, if possible.
When a return air duct is located in a wall or ceiling and requires easy access behind the grille without visible screws, access is most commonly accomplished with a two-part assembly. One part is a framed housing designed to hold both the grille and a standard-sized filter and be screwed or nailed into a return air duct opening. The second part is either (i) a hinged grille attached to the framed housing or (ii) a removable grille with hardware that “catches” movable hardware (such as rotatable latches, pins, and screws), holes or “dimples” in the framed housing.
Currently, the most common return air grille assemblies are designed using only one material, both the framed housing and the hinged or removable grille. Materials most commonly used for such assemblies are metal, such as aluminum or steel, where the assemblies are generally manufactured by “stamping” relatively thin metal, often as thin as 0.030.″ Further, HVAC systems are typically designed with sizes contemplating the use of standard-sized return air openings, standard-sized removable air filters, and correspondingly sized steel or aluminum return air grilles. For example, one industry standard-sized opening has a nominal size of 20″×25″. The actual opening in the structure is about ⅛″ to ½″ larger across the face of the opening, such as side to side, to allow the housing to fit therein. The filter size also has a nominal size also of 20″×25″ with an actual size of about ¼″ to about ½″ less across the face of the filter to fit inside the relatively thin housing. The next smaller standard-sized opening for both dimensions is 18″×20″ and the next larger standard-sized opening is 20″×30″.
In less common instances, wood or wood-like material is used, which includes both (i) the visible grille and (ii) the framed housing that affixes at the return air opening. However, current wood grille designs pose installation problems and often require additional costs associated with modifying the opening or the grille's hardware for adequate installation.
The first problem occurs when installing a wood return air grille and its wood housing in an opening designed for a standard-sized metal grille assembly. Since the dimensions of a standard-sized opening accommodate a metal grille assembly that holds a commensurate standard-sized filter, such openings do not account for the additional thickness that a wood framed housing presents, assuming the same size filter is being used. Therefore, the standard-sized opening could only accommodate a smaller wood frame and commensurate smaller filter than the prior housing and filter, thereby restricting air flow in the return air system.
For those wishing to have a wood housing and grille with at least the same size filter, existing openings must be torn out and reframed (or new openings specially dimensioned) to a larger opening size to accommodate the thicker material of the framed housing.
Renovation requires modifying the opening of the sheetrock, wood paneling, or even brick or stone, as well as the framing behind it and, in most cases, is prohibitively expensive. This is one major reason wood return air grilles are rarely found in existing homes. Even with new construction, installation problems arise from the inexperience of contractors trained to work around industry standards and norms. Often, the opening is built incorrectly and requires on-sight modifications.
In the above example of the standard-sized opening with a nominal size of 20″×25″, the extra thickness of the wood framed housing with the wood grille precludes the use of the same size filter. Thus, the structure opening would have to be torn out or a smaller standard-sized filter used, such as with an 18″×20″ nominal size. Yet, the smaller size restricts air flow and can affect performance of the entire HVAC system.
Another wood grille commercially available attempts to solve the above size problem by completely eliminating the housing and simply installing the wood grille into the structure opening without the housing. However, problems persist with this design. First, this design can require that the opening be wider than one for a metal grille assembly, thus requiring modification of the opening. An additional problem results from this design's reliance on movable clasps that can be unreliable at holding the grille in the structure opening in the event the grille is inadvertently pulled, knocked, or requires a ceiling installation.
The second problem with some existing wood air grille assemblies is that the housing frame may not easily install flush with the wall or ceiling, in contrast to the standard metal grille assembly. A standard metal grille assembly installs a housing substantially flush with the wall or ceiling, and the housing accepts the grille for attachment to the housing. With some current wood designs, there is no mechanism or design feature to prevent the housing frame from being either “pushed” beyond the plane of the wall surface or “pulled” tight with the wall surface. When using hardware that hinges, catches or locks the two components of the assembly, it is important to install the framed housing even or “flush” with the wall surface for the mechanism to connect accurately and as designed. This could cause the frame to extend from the wall, or worse, inadvertently fall out. This problem can occur with both new construction and renovations.
A related issue with existing HVAC systems and return air grille assemblies is the ease of the grille's removal for access to the filter or duct space and yet provide a secure attachment to the framed housing. This access is accomplished with either a single-piece removable grille alone or with a two-part return air grille assembly. For the single-piece removable grille that does not use a housing, the return air grille has movable hardware fasteners that (i) holds the filter to the grille and (ii) affixes directly into the opening, which requires alterations to accommodate the thickness of the grille frame and movable hardware. This type of grille uses retaining clips to snap into a rough opening without the housing, where screws must be precisely positioned on the wall framing, so these screws catch the retaining clips.
For the two-part removable assembly, there are obstacles that current designs pose in addition to practical installation challenges. Current designs of both wood and metal grilles commonly have an exposed grille frame that is larger than the return air opening to conceal the rough edges of the return air opening in the wall. However, the size of an exposed grille frame that extends beyond the housing, such as a wood grille frame, is generally too large to hinge to the smaller housing and still allow the grille sufficient space to rotate away from the housing without hitting the structure. A larger, specialty hinge would obstruct a filter's installation or removal, so that would not be an option. This size difference helps explain why current wood grille designs require the grille to be inserted straight in without angling. Such grille assemblies typically utilizes movable hardware fasteners, such as a separable snap lock or “bullet catch,” retaining clip, or the like. The grille assembly hardware must align with other hardware, such as a separable snap lock receiving end, screw, or the like, that are attached to the framed-housing component or rough opening in the wall in such a way that all the hardware fits or aligns properly to work together. Further, there is the potential cost of additional time and effort on the part of the homeowner or contractor to re-install the hardware if it is not installed properly.
A second installation challenge stems from the lack of flexibility that current designs offer if an installation error occurs. With the current design, the hardware must align precisely. Sometimes problems occur outside the grille or grille assembly itself, such as a wall framing for the return air opening being built out-of-level or out-of-square, or with the grille and/or its frame being misaligned, possibly causing the compatible hardware components to misalign and not work properly.
The third installation challenge is mitigating the potential for accidents once the grille is installed, especially when the design does not include a safety latch. Even when installed and all pieces are working properly, grilles without latches are designed to “pull out” from the return air opening or framed housing. A child holding onto the grille for support or bumping the grille could cause the grille to dislodge and fall, causing injury to the child. The potential for this problem is exacerbated by any warping or bending of the removable/retractable grille or its framed housing.
Therefore, there remains a need for an air grille assembly that can be made of thicker materials and still fit within a standardized opening, such as from a prior metal air grille assembly installation, while allowing a standardized filter to fit within the present assembly. There also remains a need for an improved securing and detachment system for the grille that minimizes manufacturing and installation costs.